African-Americans are at greater risk than Caucasians for developing hypertension, cardiovascular disease, stroke and renal disease. This is likely related to arterial dysfunction including greater arterial stiffness, and reduced microvascular reactivity of resistance arteries in African-Americans. In addition, African-Americans have higher levels of inflammatory markers, and a greater sympathoexcitatory response to various stressors. This imbalance between sympathetic and reduced parasympathetic activation may directly affect vascular function and potentiate a greater inflammatory response, further altering key structural and functional properties of the vascular wall. The overall aim of this proposal is to test the effects of endurance exercise training on arterial structure and function, and to examine potential mechanisms producing changes in arterial structure and function in young (18-35 years of age) African Americans when compared to Caucasians. We will examine these effects at rest and following a low intensity (submaximal cycle ergometry) and high intensity (maximal cycle ergometry) sympathoexcitation at both pre- and post-intervention time points, since sympathoexcitation may elucidate changes not evident at rest. Because African-Americans have higher levels of arterial stiffness, lower microvascular reactivity, greater responses to sympathoexcitation, greater levels of inflammatory markers and greater vasoconstrictive tone, we hypothesize that African-Americans will benefit more (e.g. show greater changes in response to exercise training) and retain these changes longer following de-training, when compared to a matched group of Caucasians. Our specific aims will test: 1) the effects of endurance training on arterial stiffness, conduit artery and microvascular reactivity at rest and following acute sympathoexcitation;2) the effects of endurance training on arterial remodeling;3) the effects of endurance training on autonomic function and markers of inflammation. We will utilize a longitudinal design with control, exercise and detraining periods of equal length (8 weeks). Subjects will be tested during week 0 (baseline), at week 8 (following the control period), at week 16 (following the exercise intervention), and again at week 24 (after the de-training period). Subjects will be tested on 3 different days at each testing point, to allow for measuring the response to the two different sympathoexcitatory stimuli (maximal and submaximal exercise). We will utilize a mixed-model experimental design comparing data collected on groups (African-Americans and Caucasians) and longitudinally at four time points using Piecewise Linear Multilevel Modeling. This project will have potentially large public health effects documenting the preventive effects of endurance training in African- Americans, and will provide important mechanistic insight into the role that endurance training plays in improving arterial, autonomic and inflammatory status in young African-Americans and Caucasians. PUBLIC HEALTH RELEVANCE: Vascular and autonomic function, and inflammation are predictors of cardiovascular mortality and morbidity and are precursors of, and contributors to, hypertension, CVD, stroke and renal disease. African-Americans are at greater risk than Caucasians for developing these diseases. This project evaluates the effect of endurance exercise training as a preventive behavioral intervention to lower the risk of these diseases in young African-Americans.